Atmospheric point spread function interpolation for weak lensing in short exposure imaging data

Chang, Chiway et al.
Marshall, P. J.; Jernigan, J. G.; Peterson, J. R.; Kahn, S. M.; Gull, S. F.; AlSayyad, Y.; Ahmad, Z.; Bankert, J.; Bard, D.; Connolly, A.; Gibson, R. R.; Gilmore, K.; Grace, E.; Hannel, M.; Hodge, M. A.; Jones, L.; Krughoff, S.; Lorenz, S.; Marshall, S.; Meert, A.; Nagarajan, S.; Peng, E.; Rasmussen, A. P.; Shmakova, M.; Sylvestre, N.; Todd, N.; Young, M.
Publication Date: 
Friday, June 12, 2015
Journal Articles
Monthly Notices of the Royal Astronomical Society
427 Issue 3
Page #: 
2 572
A main science goal for the Large Synoptic Survey Telescope (LSST) is to measure the cosmic shear signal from weak lensing to extreme accuracy. One difficulty, however, is that with the short exposure time (≃15 s) proposed, the spatial variation of the point spread function (PSF) shapes may be dominated by the atmosphere, in addition to optics errors. While optics errors mainly cause the PSF to vary on angular scales similar or larger than a single CCD sensor, the atmosphere generates stochastic structures on a wide range of angular scales. It thus becomes a challenge to infer the multiscale, complex atmospheric PSF patterns by interpolating the sparsely sampled stars in the field. In this paper we present a new method, psfent, for interpolating the PSF shape parameters, based on reconstructing underlying shape parameter maps with a multiscale maximum entropy algorithm. We demonstrate, using images from the LSST Photon Simulator, the performance of our approach relative to a fifth-order polynomial fit (representing the current standard) and a simple boxcar smoothing technique. Quantitatively, psfent predicts more accurate PSF models in all scenarios and the residual PSF errors are spatially less correlated. This improvement in PSF interpolation leads to a factor of 3.5 lower systematic errors in the shear power spectrum on scales smaller than ∼13 arcmin, compared to polynomial fitting. We estimate that with psfent and for stellar densities greater than ≃1 arcmin−2, the spurious shear correlation from PSF interpolation, after combining a complete 10-yr data set from LSST, is lower than the corresponding statistical uncertainties on the cosmic shear power spectrum, even under a conservative scenario.
Reviewed Under: 
LSST Publication Policy (2015 or earlier)

Financial support for Rubin Observatory comes from the National Science Foundation (NSF) through Cooperative Agreement No. 1258333, the Department of Energy (DOE) Office of Science under Contract No. DE-AC02-76SF00515, and private funding raised by the LSST Corporation. The NSF-funded Rubin Observatory Project Office for construction was established as an operating center under management of the Association of Universities for Research in Astronomy (AURA).  The DOE-funded effort to build the Rubin Observatory LSST Camera (LSSTCam) is managed by the SLAC National Accelerator Laboratory (SLAC).
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